We have experimentally investigated the interactions between floating magnetic spheres which are submitted to a vertical magnetic field, ensuring a tunable repulsion, while capillary forces induce ... [more ▼]

We have experimentally investigated the interactions between floating magnetic spheres which are submitted to a vertical magnetic field, ensuring a tunable repulsion, while capillary forces induce attraction. We emphasize the complex arrangements of floating bodies. The equilibrium distance between particles exhibits hysteresis when the applied magnetic field is modified. Irreversible processes are evidenced. Symmetry breaking is also found for three identical floating bodies when the strength of the magnetic repulsion is tuned. We propose a Dejarguin-Landau-Verwey-Overbeek (DLVO)–like potential, i.e., an interaction potential with a primary and a secondary minimum, capturing the main physical features of the magnetocapillary interaction, which is relevant for self-assembly. [less ▲]

The influence of relative humidity (RH) on the extremely slow compaction dynamics of a granular assembly has been experimentally investigated. Millimeter-sized glass beads are considered. Compaction ... [more ▼]

The influence of relative humidity (RH) on the extremely slow compaction dynamics of a granular assembly has been experimentally investigated. Millimeter-sized glass beads are considered. Compaction curves are fitted by stretched exponentials with characteristic time τ and exponent δ, which are seen to be deeply affected by the moisture content. A kinetic model, taking into account both triboelectric and capillary effects, is in excellent agreement with our results. It confirms the existence of an optimal condition at a relative humidity ≈45% for minimizing cohesive interactions between glass beads. The exponent δ is seen to depend strongly on the diffusive character of grains and voids inside the packing: diffusion for cohesiveless particles and subdiffusion when cohesion plays a role. As a consequence, the RH represents a relevant parameter that should be reported for every experimental work on a slowly driven dense random packing. [less ▲]

A series of samples have been characterized by 3D image analysis (using X-Ray microtomography). The samples consist of blends of metallic particles: steel shot abrasives (“balls”), steel fibres and ... [more ▼]

A series of samples have been characterized by 3D image analysis (using X-Ray microtomography). The samples consist of blends of metallic particles: steel shot abrasives (“balls”), steel fibres and angular steel grit particles. The blends were systematically prepared in different proportions of the raw products. Various shape and size parameters were measured on the particles: equivalent volume diameter (dV), maximum inscribed sphere diameter (dIN), particle length (maximum Feret diameter), particle elongation (El), particle flatness (Fl) etc. The results are expressed as statistical shape and size parameters, expressed both as volume and number weighted distributions. The blends have been tested for compaction using a cylindrical container which experiences a series of 500 free falls over a height of 3mm. The compaction dynamics was monitored using a sensor that measures the evolution of the solid volume fraction as a function of the tap number. From the obtained compaction curve, the Hausner ratio and a flowability index were extracted. The same blends have also been analysed using a rotating drum at different rotation speeds to analyze the evolution of the flowing angle. As the system is based on the analysis of a time sequence of 50 images (separated by 0.5 sec) it is possible to measure the intermittent character of the powder flow. The resulting measure is a cohesive index of the powder. The results obtained from physical testing were systematically plotted as a function of various statistical indices of the shape and size distributions in order to reveal correlations between particle shape properties and physical behaviour. Some clear trends appeared, demonstrating the influence of particle shape on powder physical properties. [less ▲]

The Barabasi-Albert (BA) model with ﬁnite-precision preferential attachment is used to build a wide range of network structures. Spreading epidemics and collective dynamics are investigated on such ... [more ▼]

The Barabasi-Albert (BA) model with ﬁnite-precision preferential attachment is used to build a wide range of network structures. Spreading epidemics and collective dynamics are investigated on such complex networks. Numerical simulations reveal a transition from an exponential scaling to a power law distribution of link numbers per node along with the increase of the tuning parameter ω. The collective synchronization induced by Susceptible- Infected-Recovered-Susceptible (SIRS) epidemiological process is shown to depend on the topological structure of the network. [less ▲]

A vessel is plunged upside down into a pool of 50 cSt silicone oil. An air bell is then created. This bell is vertically shaken at 60 Hz that leads to the oscillation of the air/oil interface. The edges ... [more ▼]

A vessel is plunged upside down into a pool of 50 cSt silicone oil. An air bell is then created. This bell is vertically shaken at 60 Hz that leads to the oscillation of the air/oil interface. The edges of the immersed vessel generate surface waves that propagate towards the center of the bell. When the amplitude of the oscillation increases, wave amplitude increases. We study the influence of the angle between successive sides on the wave patterns. Two kinds of vessel have been studied: a triangular and a square prism. The shape of the air/oil meniscus depends on the angle between the sides of the considered prism. As the amplitude of the oscillation is increased, the triple line, which is the contact line between the solid and the air/oil interface, moves up and down. Above a given acceleration that depends on the immersion depth and on the shape vessel, wave goes under the corner edge of the bell. During the oscillation, the wave generates at the edges presents a singularity that leads eventually to a jet and a drop ejection. A drop is ejected at each oscillation. More complicated ejection can be produced with further increase of the amplitude. This is a sample arXiv article illustrating the use of fluid dynamics videos. [less ▲]